A conventional credit card allows a user to make a purchase from a vendor by simply recording the credit card number and the user's signature on a suitable form, with actual transfer of funds therefor being made at a later time between the credit card company and the vendor. Similarly, a conventional debit or bank card allows a user to make a purchase from a vendor by authorizing a transfer of funds from a preexisting user account, such as a checking account, to the vendor. In both situations, the card itself does not contain an indication of available credit, but typically includes a magnetic strip in which is magnetically stored certain information such as account identification numbers.
Intelligent or smart cards are being developed in the size of conventional plastic credit cards, which include an imbedded computer chip therein having processing power and memory or storage capacity therein. For example, the International Standards Organization (ISO) has established certain specifications for such electronic cards under the ISO Series 7810, 7811, and 7816. The typical electronic card includes a plurality of spaced apart electrical contacts on one surface thereof which provides input and output interfaces with the computer processor and memory in the card.
One application for the electronic card is an electronic purse. In this configuration, a prepaid amount of credit or electronic currency is stored in the card memory for use in the place of conventional cash. The source of the currency installed in the card may take any suitable form such as a bank account, a credit card, a debit card, another electronic card, or other sources. In operation, the electronic card is inserted into a conventional transaction device which communicates with the card through the contacts. The transaction device would be associated with the typical cash register of a vendor, for example, so that the amount of purchase from the vendor may be directly withdrawn from the electronic card itself by correspondingly reducing the available currency stored in the card memory.
However, this arrangement provides no protection for the user from an unscrupulous vendor having a transaction device configured for withdrawing from the card more than the authorized amount. A simple analogy would entail providing the user's entire billfold or purse to the vendor who then is supposed to remove from the entire amount of currency contained therein only that amount required for the specific purchase. If the vendor is unscrupulous, more than the required purchase amount may be taken without authorization of the purchaser. Accordingly, it is desirable to have an electronic purse card limiting or preventing unauthorized access to the currency amounts stored therein.